Designs for aerospace vehicles that fly now and that will fly in the next several decades emphasize increased maneurverability, energy conservation, safety of personnel and increased ability to achieve and maintain both tactical and strategic superiority in a given theater of operations. Because of the increased performance demands being placed on aerospace vehicles many of the production materials once considered standards have been found to be inadequate; therefore, there has been an increasing emphasis on the development of composite materials because of their high strength to weight ratio. Strong, light-weight sheet materials have been developed which comprise generally a resinous sheet reinforced with layers of continuous, parallel filaments. These sheets may be formed as a single layer sheet or as multi-layer laminates and are cured to form tough, hard, exceptionally strong panels for skins.
Since the earliest days of the aircraft industry, those skilled in the art of airplane construction have searched for fasteners that could accommodate shear and tensile loading between the skin of the aircraft and the load carrying substructure. Until very recently, mechanical fasteners were used to the exclusion of all other types of fasteners to attach the skin to the substructure of an airplane. The use of mechanical fasteners in composite structures increases the cost of final assembly because of special drilling and reinforcement requirements and because fasteners used in composite applications must be made from more expensive materials to prevent serious corrosion from occurring on the finished aircraft.
The prior art as evidenced by U.S. Pat. Nos. 1,504,817; 1,519,772; 1,901,864; 2,053,048; 2,161,802 and 2,483,916 teaches stitching as a method for fastening a skin to a substructure. In these patents the artisan is taught to attach the skin to an intermediate tape that is attached to the substructure. More recent prior art, U.S. Pat. Nos. 4,206,895; 4,256,790 and 4,331,723 teach stitching as a method to join composite subparts to form a larger part. Although stitching composite joints has produced significant increases in composite joint strength, until now the process has been limited in application because all prior art composite stitching processes generally require access to both sides of the parts being joined. This requirement is a serious constraint on the size and shape of parts which may be stitched because previous methods and apparatus have required access to both sides of the part.